This disclosure relates to a retainer for a torque frame pin in a fan drive gear system.
One type of gas turbine engine includes a fan drive gear system that is interconnected between a spool of a core engine and a fan. One example the fan drive gear system is provided by an epicyclic gear train and includes a centrally located input gear driven by the spool, intermediate gears circumferentially arranged about and intermeshing with the input gear and a ring gear provided about and intermeshing the intermediate gears. The intermediate gears are mounted within a carrier, which is supported by a torque frame. Depending upon the configuration, either the torque frame or the ring gear rotationally drives the fan via a fan shaft in response to rotation of the input gear.
Each of the intermediate gears are supported in the carrier by a journal extending between spaced apart walls of the carrier. The carrier is typically constructed from a high strength metallic alloy such as steel, titanium or nickel. The torque frame is typically fixed to the carrier by a flexural pin. This pin serves two functions. First, the pin ensures that lubrication passages associated with the torque frame and carrier are properly aligned. Second, the pin precisely locates the torque frame and carrier in the desired position. The flexural pin is made from case hardened steel, such as Nitralloy® and is held in place by a retainer pin. The retainer pin is made from a deep-hardened steel alloy that can withstand high service temperatures and high stresses. Owing to its properties and material compatibility with nitrided steels, a 418 stainless steel, such as Greek Ascoloy®, is frequently chosen.
In current torque frame retention designs, the retainer pin is a unitary structure that is threaded at one end. The threaded end is received by a correspondingly threaded hole in the carrier. The other end is a cylindrical portion that is received in a slip fit relationship by a corresponding aperture in the flexural pin to align the flexural pin in a desired orientation.
The retainer pin is a high-cost part that is difficult to manufacture and is susceptible to deformation upon installation due to existing tolerances. Assembly and disassembly of the fan drive gear system currently requires torqueing the retainer. During torqueing, the retainer pin may break if the cylindrical portion of the retainer pin binds to the flexural pin. The retainer pin may then need to be removed by electrical discharge machining, which could render the carrier unusable. Additionally, it is beneficial to avoid threading a Greek Ascoloy part.